Mt Ruapehu generating hot stuff

Ruapehu Crater lake. FILE

It's shaking all over, and generating some hot stuff, but a volcanologist says it's way to soon to tell what's next for Ruapehu.

The mountain's crater lake has been heating up and volcanic tremor signals were at their most intense in nearly a decade.

However, GNS volcanologist Brad Scott said most of Ruapehu's latest behaviour was not unusual.

"Basically the crater lake's been heating up since mid-December. This is a pretty long-term process," Mr Scott said tonight.

The heating cycle normally took nine to 15 months, he said.

Mr Scott said the lake would heat during that cycle from 15C to 40C.

The lake attained high temperatures in late January then started to cool, but in the last three to four weeks temperatures shot back up, reaching the high 30s.

It was not unusual to have a "double peak" of this nature, Mr Scott said.

The tremors were not strong enough for people to feel, he said.

"Active volcanoes will record a variety of seismic signatures."

He said these included "discreet earthquakes" often too small to be felt.

"It can be generated by gas and fluids moving inside the volcano."

A reliable way of predicting how these tremors would influence "surface activity" such as eruptions was not established.

"It's slightly unusual at the moment, it's relatively strong," Mr Scott said. "It's been switching on and off for periods of two or three days for the last couple of weeks."

These volcanic tremor signals, made up of continuous ground vibrations, were at their strongest since 2006 or 2007.

Mr Scott said these vibrations were analogous to those felt on a bench with a boiling electric kettle.

"When it's boiling it's really quite rowdy ... the geothermal system in the volcano is basically doing the same thing."

GNS had a Volcanic Alert Level 1 in place, indicating only "minor unrest."

Mr Scott said this was typical for Ruapehu. The only level lower was zero, which Mr Scott joked could only be achieved if Ruapehu was filled with concrete.

Predicting what might occur in upcoming days or weeks, Mr Scott said Ruapehu could swing one of two ways.

It could "back off" or erupt but it was far too soon to tell what would happen.

There was no evidence distant phenomena such as Saturday's Nepal earthquake and last week's Calbuco eruption in Chile influenced New Zealand's volcanic activity.

Some headlines and social media comments about the crater lake were approximating panic today.

News of the heating lake followed soon after the Nepal quake and Mr Scott said some people "joined the dots" too soon.

"The social media response is an interesting sort of animal," Mr Scott said.

The current signals were similar to those in 2006 and 2007 but weaker than those recorded in 1994/1995, fellow volcanologist Art Jolly said.